Remember when environmental protection was a bipartisan effort?

A prediction: When all the votes have been counted and the reams of polling data have been crunched, analyzed, and spun, this will be clear: Few scientists will have voted for Republican candidates, particularly for national office. Survey data taken from 1974 through 2010 and analyzed by Gordon Gauchat in the American Sociological Review confirm that most American scientists are not conservatives. A 2009 study by the Pew Research Center found that only 9 percent of scientists self-identified as conservative, while 52 percent called themselves liberals. Only 6 percent of American scientists self-identified as Republicans. This state of affairs is bad for the nation, and bad for science.

It was not always this way. In the 1968 election, Richard Nixon won the votes of 31 percent of physicists, 42 percent of biologists, 52 percent of geologists, and 62 percent of agricultural scientists (compared with 43.4 percent of the popular vote). While these data do not include party affiliation, they suggest that the scientific community of the late 1960s was much more evenly divided between the two major parties than it is now, and, with the exception of physicists, slightly more conservative than the American voting public at large.

Why have scientists fled the Republican Party? The obvious answer is that the Republican Party has spurned science. Consider Mitt Romney's shifting position on climate change. As governor of Massachusetts in 2004, he laid out a plan for protecting the state's climate. As presidential candidate, he has said that climate change is real, but has questioned whether humans are causing it. His stance is consistent with the Republican Party platform, which unambiguously calls for expanding the production and use of the fossil fuels that drive climate change. In 2009, Paul Ryan accused climate scientists of "clear efforts to use statistical tricks to distort their findings and intentionally mislead the public on the issue of climate change," echoing false accusations leveled against climatologists at the University of East Anglia. Mitt Romney and Paul Ryan exemplify the conservative turn against science, but what explains it?

It seems hard to believe today, but environmental protection used to be a bipartisan affair. In the early half of the 20th century, Republican and Democratic administrations pursued conservation, setting aside land as national forests and parks but leaving pollution control to local and state governments. By the 1950s, however, pollution became a national issue. Above-ground nuclear-weapons testing spread radioactive fallout globally, along with a fear of the consequences. Rachel Carson's 1962 book,Silent Spring, documented the adverse effects of pesticides, especially DDT. Less well remembered but equally important was the work of Clair Patterson, a geochemist at the California Institute of Technology, who showed that lead pollution from cars had reached Antarctica. By 1970 it was no longer plausible to argue that pollution was a local problem—a "neighborhood effect," as the economist Milton Friedman called it in 1962.

Confirmation of global warming activated a new phase in the conservative assault.

Over the next few decades, scientists identified more problems: acid rain, stratospheric ozone depletion, anthropogenic climate change. These largely invisible threats were transnational, even global, and required scientific expertise to understand, and international coordination (if not international governance) to resolve.

Early pollution legislation, passed during the Kennedy and Johnson administrations, was relatively weak, but a growing national consensus motivated President Nixon to accept stronger measures. The National Environmental Policy Act, enacted in 1970, formalized requirements for environmental review of federal actions. The Clean Air and Water Acts, the Endangered Species Act, and the creation of the Environmental Protection Agency established a powerful new framework for environmental protection in the United States.

The historian J. Brooks Flippen has argued that so much progress was made so quickly in part due to party competition: Democrats were trying to appropriate the mantle of environmentalism from Republicans; Nixon was intent on retaining the mantle for himself and his party (although he ultimately concluded that despite winning the 1972 election he had not received enough benefit from his environmental leadership). He was also losing support from the Republican Party's traditional base of business leaders, who opposed the expansion of federal regulatory power and worried about the effect of new regulations on their businesses. Nixon resolved to recommit to business. Although his premature departure from office prevented him from having an immediate impact, he wasn't alone in believing that the GOP's future depended on realigning itself with business.

There had long been a Republican anti-New Deal coalition focused on promoting "free enterprise" and rolling back perceived restrictions on economic freedom. In the 1930s, the National Association of Manufacturers strongly opposed Roosevelt's reforms, which were seen by many business leaders as socialist. This critique was revived in the 1970s and given new vigor by a coalition of business leaders and conservative foundations, who established think tanks to promote deregulation and laissez-faire policies, based particularly on the ideas of Friedrich von Hayek and Milton Friedman.

One of the new think tanks, the Heritage Foundation, was especially influential with the Reagan administration. Conservative foundations also gave rise to an explicitly anti-environmental literature during the 1980s and 1990s. A study published in the journal Environmental Politics in 2008 found that 110 environmentally skeptical books were published between 1970 and 2005 in the United States. Only nine had no apparent connection to a conservative think tank.

These changes in Republican strategy were not just the result of a political realignment; they were also a response to a conceptual realignment in the environmental movement. Before the 1960s, land conservation included the possibility of future economic use, while land preservation focused only on shielding specific wilderness locations from development in perpetuity. Both ideals focused on protecting areas of singular natural beauty. This "aesthetic environmentalism"—as some historians call it—did not inspire, or require, a big expansion of federal authority. Nor did it rely much on science. But pollution control did require federal government action—and a lot of science. Indeed, most environmental legislation passed in the early 1970s stipulated that policies be based on the best available science. As a result, scientists became part of the newly expanded regulatory state. This occurred just as the business community and its Republican allies were organizing a counterattack.

The idea of limits is at the center of early conservationism and later environmentalism. Conservationists argued that the reckless use of resources could lead to shortages. Environmentalists insisted that it isn't just physical resources that are limited; oxygen, water and nitrogen, and the "sinks" that sequester and reprocess waste were limited, too. The idea of "Spaceship Earth," a vision of Earth as a ship with limited supplies, was popularized during the late 1960s. And in 1972 a group of systems scientists wrote the book Limits to Growth, forecasting crisis and collapse if population, resource consumption, and pollution were not reined in.

Limits to Growth was a phenomenon, selling more than 10 million copies. It was also instantly controversial, as it countered the most basic tenet of market economics: the idea that infinite growth is possible. The book claimed that natural limits to growth would be reached sometime within the next 100 years. The authors focused in part on the likely availability of some basic industrial minerals, basing their estimates on the known reserves. Critics pointed out that these estimates understated available minerals because companies stop looking for new reserves once several decades' supply has been identified—exploration is expensive and only justifiable when there is anticipated demand. Similarly, Limits to Growth ignored the role of technological innovation. (The current natural-gas drilling boom in the United States, due in part to advances in horizontal drilling, is a case in point.)

What the critics missed, and what American conservatives would studiously ignore, was that Limits to Growth was correct in one of its major claims: There are limits to the planet's capacity to absorb pollution. The book actually described two different forms of limits: limits to sources—the commodities necessary to run industrial civilization—and limits to sinks—places to store and absorb the byproducts of that civilization. Much of the debate centered around sources. In hindsight, the argument about sinks was more important.

Consider carbon dioxide. The Limits authors knew that it was a greenhouse gas that could alter the climate, and they extrapolated from a simple exponential curve that the concentration of carbon dioxide in the atmosphere would reach 380 parts per million by 2000. (They were close: It reached that level in 2006.) The authors also discussed the relationship between rapid increases of pollutants in the Great Lakes and rapid declines in fish catch, as well as the diminished amount of dissolved oxygen in the Baltic Sea due to organic waste (a later generation would begin to refer to these proliferating oceanic zones of low oxygen as "dead zones," where marine life cannot live). The authors acknowledged that these limits, except for carbon dioxide, were local not global, but they did not doubt that global limits existed—scientists simply had not yet put much effort into figuring out what they were.

It is hard to argue that the Limits authors were wrong on this point. Yet they were branded as Doomsayers by their opponents, who became known as the Cornucopians. Their intellectual leader in the United States was the economist Julian Simon, later hailed by Wired magazine as the "Doomslayer." Simon rejected the very idea of limits, and especially the notion that population growth should be restricted. Human ingenuity was the ultimate resource, he argued, and as long as it was unrestrained there was nothing humans could not accomplish. He saw pessimism at the root of American environmentalism, and he railed against it. Simon emphasized data showing improving environmental conditions, contending they were improving because Americans had become wealthier. "Wealthier is greener," his followers declared.

Wealth no doubt played some role in enabling the United States to spend money on environmental protection, but this money would not have been spent were it not for the demands of environmentalists. In his zeal to oppose the Doomsayers, the Doomslayer could not admit that the pessimists helped make his own prophecy come true. Humans are innovative, and many problems have engineering solutions, but innovation follows incentives. The Clean Air and Water Acts provided incentives to solve environmental problems. Simon's own generation of economists generally thought these laws were inefficient, and they advocated for more market-friendly reforms during the 1980s, such as emissions trading to reduce acid rain. But Simon and his followers refused to admit that the environmentalists had been at least partly correct.

Climate scientists came under attack because they had exposed significant market failures.

Conservative politicians sided with Simon and the Cornucopians. In 1984, a member of the House of Representatives from Georgia named Newt Gingrich published a book calling for huge government investment in space exploration and ultimately settlement of the moon, which was necessary, he said, to destroy the myth of limits. The solar system contains essentially limitless resources, Gingrich reasoned; thus, incorporating them into America's economic sphere would defeat the environmentalists' critique of capitalism once and for all. That same year, Herman Kahn, a founder of the conservative Hudson Institute, joined forces with Julian Simon to edit The Resourceful Earth, an explicit rejoinder to Limits to Growth. And in 1999, a coalition of conservatives created the Club for Growth to counter the Club of Rome—the group of European business leaders who had commissioned the original Limits to Growth study.

The Reagan administration also rejected the idea of limits, seeing technological innovation as the best solution to pollution. Reagan's budget director, David Stockman, set out to reduce or eliminate the regulatory burden on industry by rolling back regulations, preventing future ones, definancing enforcement agencies, and devolving enforcement to the states (which were generally less willing or able to regulate large industries and often lacked the scientific capability to do so). The Reagan administration's ideological assault on regulatory agencies left their staffs disorganized and demoralized. Budget cuts also deprived them of expertise, as specialists moved to positions outside government.

Reagan later replaced his most extreme cabinet members, but the antiregulatory, antilimits ideology did not fade away; it remained embedded in the New Right's network of think tanks, law firms, and foundations. It was now orthodoxy in the Republican Party, and when the Republicans took control of Congress in 1994, soon making Gingrich speaker of the House of Representatives, Republicans passed bills curtailing environmental laws. Even a Republican, Senator John Chafee, commented that "when all the artichoke leaves are peeled away," Republicans "are out for the Clean Air Act, the Clean Water Act, the Endangered Species Act. That is what they are gunning for." The new majority whip, Tom DeLay, tried to gut the EPA, particularly its enforcement powers. Gingrich cut off financing for Congress's science-advisory apparatus, the Office of Technology Assessment.

All this occurred while scientists were increasingly demonstrating the realities of planetary sinks. Most evident by the 1980s was acid rain. By the end of the decade, scientists had also begun to observe the warming they had predicted from rising levels of greenhouse gases. Confirmation of global warming activated a new phase in the conservative assault on environmental protection: Conservatives began to attack individual scientists and to deny the legitimacy of climate science, and sometimes even of the concept of publicly financed science. These attacks came from think tanks, industry trade organizations, and members of Congress. Scientists had their offices broken into, their e-mail stolen, and were subject to hostile Congressional investigations and subpoenas.

Climate scientists came under attack not just because their research threatened the oil industry (although it certainly did that), but also because they had exposed significant market failures.

Pollution is a market failure because, in general, polluters do not pay a price for environmental damage (and this includes not just polluting industries, like electrical utilities, but also anyone who uses a product—like gasoline—that takes up a portion of the planetary sink without paying for it). Nicholas Stern, a former chief economist at the World Bank, has declared climate change "the greatest and widest-ranging market failure ever seen."

Accepting the need to correct market failures required one to concede the need to reform capitalism—in short, to concede the reality of market failure and limits. This became increasingly difficult for Republicans during the 1990s and 2000s. Party leadership began supporting primary challenges against party members deemed insufficiently conservative, driving many moderates into retirement, and some out of the party entirely. Some Republicans who had acknowledged the reality of global warming lost their seats; others—including Mitt Romney—began to deny the problem, knowing that if they didn't they would not be electable as Republicans.

And so it was that during the decades that scientists began documenting how humans affect the natural world, the Republican Party committed itself to denying that impact, or at least denying that it required governmental response. And while in 2001 the historian William Cronon could argue that anti-environmentalism was a vote loser for the Republican Party, by the end of that decade it seemed no longer to be the case, as polls showed that rank-and-file Republicans were following party leaders in rejecting climate science.

One more factor should be acknowledged. The conservative turn against science coincided with the end of the cold war—what some called the "end of history"—defined by the triumph of market democracy. In one of history's ironies, the vast infusion of public money into scientific research during the cold war produced the knowledge that underscored the limits of capitalism. Equally important, the end of the cold war gave rise to an increasingly dogmatic belief in the efficacy of market capitalism. For some, victory was seen as justification for an uncritical triumphalism. If capitalism was the better system, then the best form of capitalism was its purest form. Before the cold war, it had been widely recognized that capitalism could fail (the lesson most economists took from the Great Depression); by the end of the 1980s, however, the lessons of the past were increasingly viewed as quaint.

It's hardly surprising, then, that natural scientists have fled the GOP. Scientific research, with its basis in observation and experience of the natural world, is rooted in the fundamental premise that when the results of our investigations tell us something, we pay heed. Economists have accepted that market failure is real, and if its consequences are serious, then remedies are needed. Even Hayek acknowledged this. Legitimate interventions in his view included preventing the "harmful effects of deforestation, of some methods of farming, or of the noise and smoke of factories," prohibiting the use of poisonous substances, limiting working hours, enforcing sanitary conditions in workplaces, controlling weights and measures, and preventing violent labor strikes. Hayek believed, quite logically, that if the government were to take on such functions, and particularly if doing so limited the freedom of particular groups or individuals more so than the population at large, then the justification should be clear (as it was in all the examples he gave).

Over the past four decades, natural scientists have given us those justifications. But over the last two decades, the Republican Party has rejected that science. In turn, scientists have rejected the Republican Party.

Erik M. Conway is a historian of science and technology. Naomi Oreskes is a professor of history and science studies at the University of California at San Diego. They are the authors of Merchants of Doubt (Bloomsbury, 201­0).